This application is directed to a foam-generating assembly for generating a foam particularly useful in preventing or extinguishing fires, and to a foam generator which is employed therein. It is also directed to a new method for generating a nitrogen-containing foam.
It is well known to use foams, and in particular foams containing nitrogen gas, to prevent or extinguish fires—see, for example, U.S. Pat. No. 6,112,819. Various constructions of apparatus for generating such foams have been devised. However, these known constructions are complicated and expensive to produce. The present inventors have developed a foam-generating apparatus which is simple in construction and inexpensive to produce, which will rapidly produce a nitrogen-containing foam of a desired expansion ratio, and which in one embodiment is sufficiently compact that it can be installed in an enclosed space, such as in an engine compartment or passenger cabin of a vehicle, airplane, boat, etc., to rapidly emit a fire preventing or extinguishing foam in the event of an impending or actual accident.
The inventive foam-generating assembly includes a foam generator and tanks which respectively contain a foamable aqueous liquid and nitrogen gas and which are connected to deliver their contents to the foam generator. The foam generator includes a header that defines a swirl chamber formed by a outer cylindrical wall, an inner cylindrical wall and a floor, and a spray nozzle is located in the center of its floor to emit a conical spray of the foamable aqueous liquid into the swirl chamber. An orifice is provided in the inner cylindrical wall to tangentially discharge nitrogen gas into the swirl chamber and around the spray nozzle and the liquid spray emitted therefrom to create a vortex flow of mixed liquid spray and gas. First and second mesh screens are provided through which the vortex flow will pass, first to provide a coarse foam and then a fine foam having the desired expansion ratio.
In one embodiment an extender tube can be positioned against the upper cylindrical wall to extend beyond the header and the first mesh screen, which can be in the form of an inverted frustoconical element, can be positioned in the extender tube, whereas the second mesh screen can be positioned across the outlet end of the extender tube. The outer cylindrical wall can have a larger diameter than the inner cylindrical wall, providing an annular ledge on which the extender tube is seated. The tanks can be spaced apart from the header and connected thereto by suitable conduits. A pressure regulator can be inserted in the gas conduit to control the pressure of gas delivered to the header.
In another embodiment, which provides a compact arrangement that enables the assembly to be installed in a compact space such as an engine compartment, the header can provide docking stations for the tanks and include passageways to deliver foamable aqueous liquid to the spray nozzle and nitrogen gas to the orifice in the inner cylindrical wall of the swirl chamber. A pressure regulator can be attached to the header to provide control of the nitrogen gas pressure delivered to the swirl chamber. An on-off control valve which can be electrically controlled can be included to allow gas to flow from the nitrogen tank to the header, e.g., when a signal is received from a sensor in the vehicle in which the foam-generating assembly is located that senses rapid deceleration of the vehicle (indicating impending crash). The tank containing the foamable aqueous liquid can include a flexible bag in which the liquid is contained, and a conduit from the nitrogen tank can be connected to the liquid tank to provide the pressure therein that causes the liquid to be delivered from the bag into the header.
The method of the invention involves tangentially flowing nitrogen gas around an expanding cone-shaped spray of foamable aqueous liquid in a cylindrical swirl chamber to provide a vortex and then passing the liquid spray and nitrogen gas through first and second spaced mesh foaming screens to provide a fine foam that can rapidly spread out from the swirl chamber and cover nearby areas to prevent or suppress fires.
The invention will now be better understood by reference to the attached drawings, taken in conjunction with the following discussion.